The staff of Brattleboro Retreat, a private mental health and addiction-treatment center, are planning to picket their employers Monday to protest what they say are unfair — and even unsafe — constraints in wages and benefits.

The facility’s expansion of services, patient load and revenues over the last two years haven’t translated into better working conditions for about 500 employees, John Callaci, a representative of the Providence, R.I.-based United Nurses and Allied Professionals union, said Friday.

Retreat spokesman Peter Albert said he’s confident that mediation will lead to contract agreements that are “respectful” of employees and also acknowledge tough economic times.

Both men agreed that the institution had only in the past two years emerged from a decade-long financial slump.

Employees made wage and benefits concessions that helped pull the facility into the black, Callaci said — and their compensation should not now be contingent on future growth, as proposed by management.

Albert responded that the profits had been primarily re-invested in clinical and medical staff.

“We would love to give raises, but they have to be within the limits of what we have in our pocketbook,” Albert said.

“Everyone at the Retreat will agree that they are working harder than ever under more difficult conditions including increased risk of being the target of patient assault,” Callaci wrote in a news release.

The Retreat, founded in 1834, describes itself online as “the region’s foremost provider of mental health and addiction treatment services.”

Inpatient admissions have grown from 1,952 in 2006 to 2,987, according to the website.